Current evidence suggests that administration of vasodilator agents to the circulation of skeletal muscle may actually decrease tissue oxygen levels. I propose to extend my investigations of the effects of vasodilation on oxygen delivery by measuring microvascular oxygen transport in the hamster cheek pouch and cremaster muscle during vasodilation induced by elevated carbon dioxide levels and striated muscle stimulation (metabolic vasodilation). Photographs of the microvascular architecture will be made with a 35 mm microscope camera, and measurements of blood vessel diameter, length and branching pattern from arterial through venous vessels in control and graded vasodilated states will be made from photomontages of th vasculature. Red cell velocity will be measured in these same vessels by the dual-slit photometric technique. These data will be coupled with measurements of microvessel blood oxygen content to specify the hemodynamic component of oxygen delivery. The partial pressure of oxygen will be measured with oxygen microelectrodes and intrasvascular hemoglobin oxygen saturation will be determined by a video densitometric technique. The flux of oxygen from blood to tissue will be measured from arterial and venous vessels as well as capillaries and the relative amounts of oxygen exchanged across each class of vessels will be determined in control and vasodilated states. Alterations in the vascular distribution of oxygen flux and tissue oxygne profiles will be assessed during application of vasodilator drugs, changes in blood and tissue carbon dioxide pressure and muscle stimulation. both animal preparations contain parallel arterial and venous blood supplies which exhibit shunting of oxygen. The relative importance of shunting on tissue oxygen supply will be examined and the influence of vasodilation on this phenomenon will be assessed. Reflected light microscopy will be utilized when these studies are extended to a relatively undisturbed skeletal muscle preparation. In summary, the experimental and analytical techniques employed in this study will provide a description of both local and global oxygen exchange which can be compared with previous whole tissue studies.